Electrical power distribution systems often include overhead electrical power distribution lines mounted upon poles by a wide variety of mounting structure. Other distribution systems include underground distribution lines in which protected cables run under the ground surface. It is often necessary to take phase-to-phase or phase-to-ground voltage measurements across distribution and transmission lines while testing for induced or live power line or equipment.
Known high voltage safety line detectors, meters and testers comprise high resistance probes connected in series with a calibrated panel meter to read the voltage across the phase-to-phase or phase-to-ground terminals. They are designed for use as safety tools by high voltage line maintenance workers to verify the status of the line or equipment as nominal, induced or de-energized.
A DC high potential (HIPOT) test has been used to test the serviceability of underground AC high voltage power cables before the cables are placed in service at a substation and distribution electric lines of the power system. The DC HIPOT test is applied to the cable to verify that the cable is good for high voltage use. To conduct the test a high DC voltage is placed across the cable conductor and shield. The test is performed to ensure the status of the cable insulation, whether it is good or faulty before placing the cable in service.
One known high voltage DC HIPOT test meter comprises a high voltage phasing meter along with a high voltage diode. The high voltage diode is placed in series with one of the meter probes. The DC high voltage is converted from the high voltage AC by use of the high voltage diode. The phasing meter can then be used as a cable testing device. The high voltage diode may consist of a plurality of high voltage diodes connected in series, as shown in FIG. 4. This is done to ensure that the diodes can withstand the required voltages during the reverse bias state. Advantageously, there should be a uniform voltage distribution across each high voltage diode. However, stray capacitance between the diodes to the ground, as shown in FIG. 4, creates instability. The voltage stress will not be uniform across each diode due to stray capacitance. The voltage stress will be more than double the uniform stress at the diodes near to the high voltage side. This leads to degradation of the diodes at the high voltage side. This can result in failure of the string of diodes over the period of operation so that the system may become non-performing.
The disclosure is directed to improvements in DC high potential testing meters.